The world is now very likely to breach the 1.5°C global warming threshold within the next decade – but rapid cuts to emissions could still limit the damage, according to the United Nations Environment Programme.
UNEP says the focus must now shift towards making any overshoot of the Paris Agreement target as small and short-lived as possible.
Its modelling suggests rapid action could limit the temperature overshoot to around 0.3°C with a 66% probability and bring global temperatures back towards 1.5°C by the end of the century.
That would require global greenhouse gas emissions in 2030 to be 26% below 2019 levels and 46% lower by 2035.
Current policies remain far off that trajectory.
UNEP estimates existing measures are consistent with warming of up to 2.8°C this century, while the latest national climate pledges would still leave the world heading towards around 2.3°C to 2.5°C.
The report places much of the immediate challenge on transforming the global energy system.
UNEP says the technologies needed for substantial emissions reductions already exist, with wind and solar expanding rapidly and deployment costs continuing to fall.
Faster electrification, renewable generation, improved efficiency and reduced fossil fuel use could therefore determine not only whether temperatures overshoot 1.5°C but how far and for how long.
Delaying emissions cuts would also leave governments increasingly reliant on removing huge quantities of carbon dioxide from the atmosphere later this century.
UNEP estimates reversing every additional 0.1°C of warming could require carbon removal equivalent to around five years of current global annual CO2 emissions.
Those technologies remain uncertain, expensive and difficult to deploy at the necessary scale.
The agency warns even temporary overshoot matters because additional warming raises the risk of irreversible changes including ice-sheet loss and damage to ecosystems that would not necessarily recover if temperatures subsequently fell.
The gap has narrowed since the Paris Agreement was adopted, when projections pointed towards 3°C to 3.5°C of warming.
But UNEP says the remaining reductions now need to happen much faster.
The message is that breaching 1.5°C no longer means the target becomes irrelevant.
Every fraction of a degree avoided reduces climate damage, lowers future carbon removal requirements and cuts the risk of triggering changes that cannot be reversed.
